The insertion of animal parts into human beings goes back at least to 1682, G. Wayne Miller reports in The Xeno Chronicles: Two Years on the Frontier of Medicine Inside Harvard's Transplant Research Lab (PublicAffairs, $26), when a Russian nobleman wounded in battle had his skull patched up with pieces of dog bone. "The experiment was cut short," Miller writes, "when the Orthodox Church threatened the man with excommunication on the grounds that no true Christian could have part of a dog in his head. Rather than be forced from the church, the man had the bone removed." In the less doctrinaire 20th century, however, the transplantation of nonviable animal parts into humans has become commonplace: Valves from pigs, for example, are widely used to replace faulty valves in human hearts. But, as Miller re-emphasizes, these introduced valves are not living tissue. The next step is to transplant living organs from animals, a process called "xenotransplantation."

Transplanting animal parts of any kind into humans runs afoul of a medical obstacle: the propensity of the human immune system to reject foreign matter. Immunosuppressive drugs can help, but researchers at Harvard University have attacked the problem from a different angle: trying genetically to engineer pigs with a built-in immunity, so to speak, to the human immune system. Those who question the morality of such techniques are less apt to be worried about the humans helped than about the animals sacrificed, arguing that the latter are being unjustly exploited. Such detractors have ridiculed xenotransplantation in cartoons, in one of which a patient "has grown a curly tail that he isn't aware of yet. 'Side effect?' 'What side effect?' the patient says." A task force set up by the Catholic Church, however, has given its imprimatur to the procedure, noting that God has placed animals "at the service of man."

Be that as it may, the researchers profiled in Miller's book have gone ahead, breeding pigs that they think will yield living tissue that baboons will not reject after transplantation. A staff writer at the Providence Journal, Miller tells the story of this research and its leading figure, David H. Sachs, as he races to finish his controversial experiments before funding runs out.

-- Dennis Drabelle